HAYNES^® 556^® alloy is second in resistance only to HAYNES^® HR-160^® alloy to the types of sulfur-bearing environments that are present in many high-temperature industrial processes. This is due partly to its comparatively low nickel content coupled with the important addition of cobalt, the high chromium level, and the carefully balanced minor elements. For comparison, data illustrating the relative sulfidation resistance of INCONEL^® alloy 601, HASTELLOY^® X alloy, alloys 600 and 800H, and Type 310 stainless steel are shown in the accompanying photomicrographs. 556 alloy had little sulfide penetration or wastage after 215 hours of exposure in an Ar+5%H₂+5%CO+1%CO₂+ 0.15%H₂S+0.1%H₂O test gas at 1800°F (980°C). By contrast, alloys such as INCONEL alloy 601 were completely destroyed, while other materials suffered severe wastage and sulfide penetration or pitting.